The present invention relates generally to radar systems, and more specifically the invention pertains to a clutter reduction system for improving radar receiver performance.
The are several fundamental limitations to radar target detection performance. For example, signal dynamic range is defined to be the ratio of the largest to the smallest signal (variance) presented to the analog to digital converter, Signal dynamic range is determined primarily by the magnitude of the clutter return as compared to that of the target plus noise. The purpose of this invention is to reduce the clutter component of the signal prior to digitization, thus reducing the dynamic range requirement of the analog to digital converter. Improved radar performance is equivalent to increased target detection probability (for a given probability of false alarm) and is accomplished through reduced analog to digital converter probability of saturation, and increased subclutter visibility.
The task of reducing the clutter of radar systems is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 3,611,369 issued to Maguire;
U.S. Pat. No. 3,894,219 issued to Weigle;
U.S. Pat. No. 4,003,052 issued to Adelman;
U.S. Pat. No. 4,104,631 issued to Weigle; and
U.S. Pat. No. 4,586,043 issued to Wolf.
The patent to Weigle (631) teaches a clutter elimination system by integrating signal returns over different half look periods. The patent to Maguire (369) teaches a quantizer system which includes automatic clutter elimination in each of a plurality of annular sectors under surveillance. The patent to Weigel (219) teaches a comb filter as a clutter canceller. The patent to Wolf (043) teaches a distribution sensitive constant false alarm rate (CFAR) processor for deriving the clutter threshold level from the average magnitude of echo return signals. The patent to Adelman (052) teaches the use of a moving target indicator (MTI) for reducing low frequency clutter signals.
Conventional methods for reducing signal dynamic range in radar receivers include the use of hard limiters, limiting amplifiers, and logarithmic amplifiers. Sensitivity Time Control and (Instantaneous) Automatic Gain Control also reduce the likelihood of receiver saturation. However, all of the above techniques degrade performance for the detection of weak signals in the presence of strong interference. The subject invention provides an alternate technique to reduce signal dynamic range, through analog clutter cancellation.